As a conventional solid-state imaging device, a solid-state imaging device in which a charge storage portion is formed between each of the pixel portions that generates electrical charges according to an amount of received light and a charge detecting portion to which the electrical charges generated in the pixel portions are transferred and which generates a signal voltage according to the amount of the transferred electrical charges so as to enable resolution to be switched is known. In this solid-state imaging device, an offset gate portion is formed between the charge storage portion and the charge detecting portion so as to improve the detection accuracy of the signal voltage generated in the charge detecting portion.
The offset gate portion includes an N type offset gate layer formed on a surface of a P type well layer formed on a surface of a semiconductor substrate and an offset gate electrode formed on the offset gate layer.
Since a plurality of pixel portions are connected to such an offset gate portion with the charge storage portion interposed, the offset gate layer is formed by injecting impurities over a wide range of regions of the surface of the well layer.
However, when the offset gate layer is formed over a wide range of regions, a deepest portion of electric potential is formed in a central portion of the offset gate layer. That is, when the offset gate layer is formed over a wide range of regions, a potential dip is formed in the electric potential of the central portion of the offset gate layer. Thus, the transfer characteristics of the electrical charges in the offset gate portion may deteriorate.
Further, when a relative position of the offset gate electrode in relation to the position of the offset gate layer is shifted, a potential dip or a potential barrier is formed in the electric potential between the offset gate portion and a transfer gate portion formed between the offset gate portion and a charge storage layer. Thus, the transfer characteristics of the electrical charges between the offset gate portion and the transfer gate portion may deteriorate.